The dyes to be used in the ink are required to exhibit a high solubility in solvents, allow a high density recording and have a good hue and an excellent fastness to light, heat, air, water and chemical, a good fixability to image-receiving materials, difficulty in bleeding, an excellent preservability as ink, no toxicity and a high purity and be available at a low cost. However, it is extremely difficult to seek coloring agents meeting these requirements to a high extent. In particular, dyestuffs having a good cyan hue or magenta hue and an excellent fastness have been keenly desired.
In recent years, with the spread of computers, ink jet printers have been widely used to print on paper, film, cloth, etc. at offices as well as at home. Examples of ink jet recording method include a method which allows a piezoelectric element to give pressure that causes a droplet to be ejected, a method which comprises heating the ink to generate bubbles, causing a droplet to be ejected, a method involving the use of ultrasonic wave, and a method which uses electrostatic force to suck and discharge a droplet. As inks for these ink jet recording methods there are used aqueous inks, oil-based inks and solid (melt type) inks. Among these inks, aqueous inks are mainly used from the stand point of producibility, handleability, odor, safety, etc.
As dyestuffs to be used in ink for ink jet recording, too, those satisfying the aforesaid requirements have been desired, and various dyes and pigments have been already proposed and practically used. However, it is the present situation that no dyestuffs that satisfying all the requirements have been found yet. Known dyes and pigments provided with color index (C.I.) can difficultly satisfy both the hue and fastness requirements for inks for ink jet recording. As a dye which can enhance fastness there has been proposed an azo dye derived from an aromatic amine and a 5-membered heterocyclic amine described in JP-A-55-161856. However, these dyes have an undesirable hue in the yellow and cyan ranges and thus are disadvantageous in that they deteriorate color reproducibility. JP-A-61-36362 and JP-A-2-212566 disclose inks for ink jet recording for the purpose of accomplishing both hue and light fastness. However, the dyestuffs used in these publications have an insufficient water solubility when used as water-soluble ink. Further, the dyestuffs described in these publications are disadvantageous also in wet heat fastness when used as water-soluble ink for ink jet. As means for solving these problems there have been proposed a compound and an ink described in JP-T-11-504958. Further, an ink for ink jet recording which comprises a pyrazolylaniline azo dyestuff to improve hue and light fastness is described in Japanese Patent Application No. 2000-80733. However, these inks for ink jet recording leave something to be desired both in color reproducibility and fastness of output image.
Further, on the other hand, inks having improved ejection stability during image recording and little image bleeding have been desired. For example, JP-A-58-74761 and JP-A-60-92369 propose an ink comprising a dye, glycerin, diethylene glycol and an ethylene oxide adduct of alcohol and JP-A-2000-265098 proposes an ink comprising an ethylene oxide adduct of long straight-chain alcohol, but these inks leave something to be desired and are disadvantageous in that the quality of the image formed is deteriorated during storage. Moreover, JP-A-6-88048, JP-A-8-333532, JP-A-8-333533, and U.S. Pat. Nos. 5,837,043 and 5,626,655, etc. propose that the use of an ink comprising an ethylene oxide adduct of higher alcohol makes it possible to reduce image bleeding, but this ink is disadvantageous in that it still easily causes clogging and exhibits a deteriorated image preservability after printed, resulting in tone change.
Further, it was made obvious that there are some cases where an image recorded on a gloss paper of photographic image quality dedicated to ink jet recording exhibits a remarkably poor preservability when put on the wall of an indoor room. This phenomenon is remarkable particularly with gloss paper of photographic image quality dedicated to ink jet recording and thus raises a great problem with the current ink jet recording process, which is required to provide a desired photographic quality image as one of important features. The present inventors presume that this phenomenon is attributed to some oxidizing gases such as ozone in the air because this phenomenon no longer occurs when the flow of air is blocked by enclosing the printed matter in a glass frame or otherwise.